1. Field of the Invention
The disclosure generally relates to an electronic device and a matching circuit, and more particularly, relates to an electronic device for processing radio frequency (RF) signals and a matching circuit for providing variable impedance.
2. Description of the Related Art
Compact portable devices usually have smaller antennas, resulting in poor antenna performance and OTA (Over-The-Air) performance. There are two main methods to solve the problem. One is to enhance antenna efficiency, and the other is to increase antenna bandwidth.
FIG. 1 is a diagram illustrating a traditional matching circuit 100 with variable impedance. As shown in FIG. 1, an antenna 102 is coupled to the matching circuit 100, which includes inductors 104, 110 and variable capacitors 106, 108. With different capacitances, the variable capacitors 106, 108 are the primary tuning elements to increase the antenna bandwidth. Different capacitances can be obtained according to controlled voltages of the variable capacitors 106, 108. However, the impedance of the matching circuit 100 cannot be tuned by the inductors 104, 110, such that freedom of design is limited.
Furthermore, U.S. Pat. No. 4,564,843, “Antenna with P.I.N. diode switched tuning inductors”, discloses a tuned radio antenna for a frequency agile communication system. According to FIG. 2 of the patent disclosure, the tuned radio antenna has a plurality of tuning inductors in series with a short-circuiting switch for each inductor. The plurality of tuning inductors are configured to provide variable impedance. However, each tuning inductor has small inner resistance. When coupled in series, all resistance of these tuning inductors is summed up. The total resistance increases signal transmission loss.